Tipton, K. (2009). Nutritional strategies to increase muscle mass and function in athletes. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

"Appropriate muscle mass and function are critical for athletes. Nutrition influences the impact of training on muscle mass and function. In particular, protein intake is often considered to be the most important nutritional factor. The metabolic basis for changes in muscle mass is the balance between protein synthesis and breakdown of muscle contractile proteins. The net balance between synthesis and breakdown over any given time determines changes in muscle mass. Accretion of muscle proteins occurs during periods of positive balance, that is, when synthesis exceeds breakdown, and muscle proteins are lost during periods of negative balance. Exercise and nutrition influence muscle mass through changes in muscle protein synthesis and breakdown that will increase (or decrease) the net balance. On a daily, or even hourly, basis the net balance can be either positive or negative, depending on feeding and exercise situations. The length and duration of these periods of positive and negative balance determine the net loss or gain of muscle mass. Nutritional influences on muscle mass have received a great deal of attention lately. It is clear that protein ingestion is critical for increased muscle mass. Muscle protein balance can be improved by exercise alone, but without a source of amino acid the net balance does not reach positive levels. Thus, protein and amino acids in various forms are generally thought to be the most important nutrient for muscle building. However, the optimal amount of dietary protein for optimization of muscle mass remains unclear. Furthermore, it is clear that factors other than the total amount of protein in the diet influence muscle mass and function. The latter include energy intake, intake of other nutrients, timing of nutrient intake and the interaction of these factors. In particular, energy balance seems crucial for gains in muscle mass. Carbohydrate intake is often overlooked by those desiring increased muscle mass. However, carbohydrate intake must be sufficient to support appropriate training. Recent evidence suggests that glycogen levels may help determine the response of muscle to exercise. Whereas most of the attention on muscle mass has been given to gaining muscle, athletes in many situations may want to maintain or even lose muscle mass. Nutritional interventions may help to influence the adaptations to particular situations. Furthermore, muscles that are immobilized due to injury will atrophy. Minimizing the atrophy during forced disuse and optimizing regain of muscle during recovery are crucial for returning an athlete to competition as quickly as possible. Metabolic changes during disuse atrophy may influence the nutritional strategy to optimize recovery. Protein is important, but energy intake must be carefully considered. Finally, use of particular amino acids, such as leucine may be a method to help reduce muscle loss during immobilization."

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